Image distortion can be caused by optical effects originating from a lens of a camera that acquired the image. However, it could also be caused by inadequate positioning of the camera with respect to the scene being imaged. In the former case, the distortion is optical because it is an aberration caused by the lens' physical parameters. In the latter case, the distortion is simply referred to as perspective distortion.
In luminaires that have a camera mounted therein, a large field of view is typically desired to image a large portion of a roadway, a sidewalk, a park, or generally speaking, an area around the luminaire. This is typically achieved using a wide angle lens, which inherently introduces optical distortion. In a wide angle lens camera, the field of view of the lens is much larger than the size of the image sensor of the camera. As such, the image appears squeezed to fit the pixel array of the sensor. In the distorted image, straight lines appear curved, with the effect being more extreme at the edges of image.
While a large field of view is desired for a camera mounted in a luminaire, performing video or image analytics on a distorted image may not yield relevant information. For example, running traffic estimation algorithms (or any other image analytics) on the edge of a distorted frame may not yield accurate results. Thus, video or image post-processing methods are not effective without mitigating the field-of-view versus distortion trade-off.
Furthermore, when a camera is used in a luminaire, a desired result can be the monitoring of specific areas of a scene, rather than the whole field of view. For example, using a camera in the luminaire, one may wish to simultaneously monitor car parking spots, crosswalks, building entrances, etc. that are in the vicinity of the luminaire or far away from the luminaire. This requirement has usually been addressed with a camera having a wide angle lens in order to capture the whole scene, and this solution is prone to optical distortion as well, as explained above.
Another option has also been to use distributed cameras, each acquiring a small image of the scene to subsequently stich all the small images together in order to obtain a large image representative of the whole scene. This solution is not only computationally intensive, since a plurality of images have to be put together, but it may also be prone to distortion when a particular area of interest is far away from the luminaire, in which case a wide angle must be used in at least one of the distributed cameras.